Chapter 7: depth and size perception

week 7

cue approach to depth perception

depth perception results from 3 sources of information

1. monocular cues to depth present in the image

2. binocular cues from the comparison of images in each eye

3. cues from focusing the eyes (vergence, accomodation)

monocular depth cues

depth cues that require only 1 eye

pictorial cues

information about depth that can be inferred from a static picture

movement based cues

cues about depth that can be seen with a single eye in which the inference of distance comes from motion

occlusion

a visual cue that occurs when one object partially hides or obstructs the view of a second object

• infer that the hidden object is further away from us than the object that obstructs it

relative height

objects closer to the horizon are seen as more distant

relative size

the more distant an object is, the smaller the image on the retina will be

familiar size

knowing the retinal size of a familiar object at a familiar distance allows us to use that retinal size to infer distance

linear perspective

pictorial depth cue that comes from the fact that parallel lines seem to converge as they recede into the distance (train tracks)

texture gradient

monocular depth cue

textures become finer as they recede in the distance

atmospheric perspective

pictorial depth cue

objects in the distance appear blurred and tinged with blue

shadows

angle of the shadow can give info on how far the object is in front of the background

motion parallax

monocular depth cue

relative velocities of objects moving across the reinae of a moving person

deletion

gradual occlusion of a moving object as it passes behind another object

accretion

gradual reappearance of a moving object as it emerges from behind another object

optic flow

perception of objects as we move forward or backward

• objects get bigger as they get closer

• faraway objects move slower than close

(con)vergence

inward bending of the eyes when looking at closer objects

stereopsis

the sense of depth we receive from the visual systems processing of the comparison of the 2 different images from each retina

binocular density

our 2 eyes are in diff locations in our head

have different views of the world

corresponding points

a point on the left retina and a point on the right would coincide if the 2 retinae were superimposed

noncorresponding points

point on left retina would not coincide with right retina if superimposed

horopter

region in space where 2 images from an object fall on corresponding locations on the 2 retinae

panums area of fusion

region of small disparity around the horopter where the 2 images can be fused into a single perception

diplopia

double images/ seeing 2 copies of the same image

results from images of an object having too much disparity to lead to fusion

crossed disparity

direction of disparity for objects is closer to the view than the horopter

→ image in the left eye is to the right of the imagine of the object in the right eye

uncrossed disparity

direction of disparity for objects that are farther from the viewer than the horopter

→ image of object in left eye is to the LEFT of the image in the image of object in the right eye

zero disparity

retinal images fall along corresponding points

object is along the horopter

correspondence problem (depth perception)

can’t determine which image in one eye matches the correct image in the other eye

random dot stereograms

images consist of a randomly arranged set of black and white dots

right and left eye images arrange identically except that some of the dots are moved to the left or right in 1 of the images

creates either crossed or uncrossed disparity

binocular cells

2 receptive fields

1 for each eye

match images coming to each eye

size-distance invariance

relation between perceived size and perceived distanced

• perceived size depends on perceived distance

• perceived distance may depend on perceived size

visual angle

angle of an object relative to the observers eye

size constancy

object seems to have a fixed size despite changing in the size of the visual angle that accompanies changes in distance

muller lyer illusion

line that has 2 lines going away at an angle looks longer than a line of the same length but the end lines angle back

ponzo illusion

2 horizontal lines are drawn (1 above the other)

both lines are on top of 2 inward angled vertical lines

top line looks longer 

ames room

2 people of the same size standing in the 2 back corners will look very different in height

moon illusion

moon looks bigger when it’s near the horizon than it does overhead